Rolling apparatus for plastic film

ABSTRACT

A wrinkleless plastic film having excellent quality without the reduction of width can be manufactured with high productivity using a rolling apparatus in which a plastic film is rolled stepwise at two rolling deformation points formed by two driving rolls and a follower roll, which rolls are brought into continuous contact with each other along the passage of the plastic film and said follower roll is driven by the rotation of said two driving rolls.

BACKGROUND OF THE INVENTION

1 . Field of the Invention

This invention relates to a rolling apparatus for a plastic film. Moreparticularly, the invention relates to an improved rolling apparatus inwhich various deficiencies in a high ratio of rolling operation withconventional apparatus have been eliminated to produce plastics films ofexcellent quality without generating wrinkles or the like with highproductivity.

2. Discussion of the Prior Art

As described, for example, in Japanese Utility Model Laid-openPublication No. 52-135465, the rolling of a plastics film is the processin which a plastic film is passed through a pair of rolls to be reducedin thickness under pressure. The rolling action is substantially causedto occur at the deformation point at which the pair of rolls are broughtinto contact and which point extends in the longitudinal direction ofthe rolls.

The above-mentioned gazette discloses that when the peripheral speeds ofa pair of rolls are made different and a plastic film is fed between therolls so as to bring the film into contact with the surface of a lowerspeed roll, reliable rolling action can be done at the deformationpoint, the rolling ratio is improved and the occurrence of wrinkles orwaving of the plastic film can be avoided.

In order to carry out the rolling at a high rolling ratio with aconventional rolling apparatus, however, it is necessary to impart highpressing force to the pressure rolls, thereby causing the followingproblems. That is, the bursting of plastic films to be rolled is liableto occur due to the applied high pressure, the deflection of rolls isbring about due to the deformation resistance of a plastic film, andwrinkles or folds in the film is caused to occur due to the difficultyin the feeding of plastic film into the deformation point.

It is, therefore, the object of the present invention to provide arolling apparatus for a plastic film which is capable of producing aquality plastic film with high productivity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front view of an embodiment of a rolling apparatus for aplastic film in the present invention;

FIG. 2 is an enlarged front view of a part of the rolling unit of theapparatus shown in FIG. 1;

FIG. 3 is an enlarged front view of pressure rolls in according with thepresent invention;

FIG. 4 is a front view of a first modification of the pressure rollsshown in FIG. 3;

FIG. 5 is a front view of a second modification of the pressure rollsshown in FIG. 3;

FIG. 6 is a front view of a third modification of the roll shown in FIG.3;

FIG. 7 is a front view of another embodiment of pressure rolls of therolling apparatus for a plastic film in accordance with the presentinvention; and

FIG. 8 is a front view of a modification of the pressure roll shown inFIG. 7.

SUMMARY OF THE INVENTION

The rolling apparatus for plastic film in the present invention ischaracterized in that at least three pressure rolls are disposed alongthe passage of a plastic film. One deformation point is formed betweentwo rolls out of the three rolls. Furthermore, the above at least threerolls form plural deformation points so as to roll the plastic filmstepwise.

The above problems in the conventional rolling apparatus such asdescribed above are caused to occur to carry out the rolling at a highrolling ratio by utilizing only one rolling deformation point. Accordingto the present invention, the rolling is carried out by utilizing pluralpoints of deformation which are formed along the passage of a plasticfilm. It is thus possible to achieve the rolling at a high rolling ratioas a overall process while conducting the rolling at a low rolling ratioin each roll deformation point. As a result, it is possible to carry outthe rolling of a plastic film without generating wrinkle or the liketogether with to attain the high productivity.

In the above-described rolling apparatus of the invention, it isdesirable that the rolling apparatus is provided with drive means todrive the above-mentioned at least three rolls, two rolls defining eachdeformation point are driven at different peripheral speeds and the rollwith a higher peripheral speed is applied to one side surface of aplastic film at one rolling deformation point and another roll with alsoa higher peripheral speed is applied to the other side surface of theplastic film at another rolling deformation point. Thus, one side andthe other side of the surface of the plastic film are alternatelysubjected to tensile stresses, thereby enabling to prevent the plasticfilm from curling, which has been caused in the conventional rollingoperation carried out with a single deformation point.

In addition to the above described features, it is desirable to arrangethat the foregoing at least three rolls are so located as to formsuccessive rolling deformation points. Thus, in a preferred form of therolling apparatus, it is possible to provide two rolling deformationpoints with only three pressure rolls.

It is particularly desirable to use two driving rolls out of the atleast three rolls and follower roll or rolls are disposed between thetwo driving rolls and driven by them. It is thus necessary to drive onlytwo rolls and the remaining rolls are driven by means of the contactwith the driving rolls.

In addition to the above described features, it is desirable to providea means to give pressing down force, in which one of two driving rollsis pushed toward the other roll in order to impart press-down force orthe above-mentioned follower roll is pushed toward the two driving rollsin order to impart press-down force. With this system, only two pressurerolls are required to be driven. In addition, the press-down forceproviding means can be made simple.

In the above rolling apparatus, the at least three rolls can also bemade up of even-numbered rolls arranged in pairs. In this case, it isdesirable to incorporate the means to give pressing down force, by whichone of the paired rolls is pushed toward the other roll to impart thepressing down force.

Furthermore, the present invention provides a rolling apparatus for aplastic film which is characterized in that the apparatus comprises anupstream side driving roll, a downstream side driving roll which isdriven at a higher peripheral speed than that of the upstream sidedriving roll, and a follower roll which forms an upstream sidedeformation point with the upstream side driving roll to effect rollingof a plastic film while forming a downstream side deformation point withthe downstream side driving roll to effect further the rolling ofplastic film once rolled at the upstream side deformation point.

Furthermore, the present invention provides a rolling apparatus for aplastic film which is characterized in that the rolling apparatuscomprises a upstream side driving roll, a downstream side driving rollwhich is driven at a higher peripheral speed than the upstream sidedriving roll, an upstream side follower roll which forms an upstreamside deformation point with the upstream side driving roll to effectrolling of a plastic film and a downstream side follower roll whichforms a middle deformation point with the upstream side driving roll toeffect further the rolling of plastic film once rolled at the upstreamside deformation point while forming a downstream side deformation pointwith the downstream side driving roll to effect still further therolling of plastic film once rolled at the middle deformation point.

In addition, the present invention provides a rolling apparatus for aplastic film which is characterized in that the apparatus comprises apair of upstream side pressure rolls to effect the rolling of plasticfilm, a pair of downstream side pressure rolls to effect further therolling of the plastic film once rolled with the upstream side pressureroll and driving means to drive the pair of the upstream side pressurerolls in such a manner that the peripheral speed of a roll on one sideis larger than that of the other pressure roll on the other side as wellas to drive a pair of the downstream side pressure rolls in such amanner that the peripheral speed of the roll on one side is larger thanthat of the other roll on the other side.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings, the present invention will be described inthe following.

FIG. 1 shows a front view of a rolling apparatus of a plastic film inaccordance with one embodiment of the present invention. FIG. 2 is anenlarged view of a rolling unit as a part of the rolling apparatus shownin FIG. 1.

In FIG. 1, the rolling apparatus 10 includes a frame 12, a preheatingunit 14, and a rolling unit 16. The preheating unit 14 is equipped witha driving motor 17 and preheating rolls 18, 19, 20, 21 and 22. Thepreheating rolls 18, 19, 20, 21 and 22 are driven by the motor 17through pulley or belt device 24. A plastic film 26 is preheated bymeans of the preheating rolls 18, 19, 20, 21 and 22, which rolls are fedwith heated fluid (not shown). The plastic film 26 is nipped by thefinal preheating rolls 21 and 22 and it is delivered to the rolling unit16.

As shown in FIGS. 1 and 2, the rolling unit 16 includes three rolls 28,30, 32 which are successively disposed in the vertical direction. Thepressure rolls 28 and 32 are mounted with nip rolls 34 and 36,respectively.

The roll 28 located in the upper side is a driving roll of lowerperipheral speed and the roll 32 located in the lower side is a drivingroll of higher peripheral speed. The roll 30 in the middle position is afollower roll so that it is rotated freely and it is driven to rotatevia the plastic film 26 by the contact with the rolls 28 and 32. Thisintermediate follower roll 30 is small in diameter as compared withthose of the driving rolls 28 and 32.

The lower peripheral speed driving roll 28 is driven by the motor 38 viaa pulley or belt device 40. In this case, the pulley or belt mechanism40 may include a variable speed multistage pulley or a gear box.Likewise, the higher peripheral speed driving roll 32 is also driventhrough another pulley or belt mechanism (not shown). The rolling of theplastic film 26 is carried out with a heating fluid (not shown) which isfeed into the lower peripheral speed driving roll 28 and the higherperipheral speed driving roll 32 to heat it.

The end frame 16a of the rolling unit 16 is provided with a slide guide42 extending vertically. A lower press-down block 44, a middlepress-down block 46 and an upper press-down block 48 are slidablyengaged in the slide guide 42. The press-down wheel 50 is connected tothe upper press-down block 48 via a feed screw mechanism 52. The lowerpress-down block 44 is usually kept at a fixed position in thevertically downward direction. The middle press-down block 46 and theupper press-down block 48 are movable perpendicularly in relation to thelower press-down block 44.

In FIG. 2, the shaft 32a of the higher peripheral speed driving roll 32which is located on the lower side is attached to the lower press-downblock 44 via a bearing and the shaft of the lower peripheral speeddriving roll 28 which is located on the upper side is attached to theupper press-down block 48 via a bearing. Therefore, the follower roll 30and the lower peripheral speed driving roll 28 are movableperpendicularly together with the associated blocks. Thus the action topress down the lower peripheral speed driving roll 28 to the followerroll 30 and to the higher peripheral speed driving roll 32 by means ofoperating the press-down wheel 50, enables to generate the pressing downforce. While, the pressing down force can also be imparted by means of ahydraulic mechanism or the like.

The nip rolls 34, 36 are supported by means of a supporting mechanismincluding, for example, an air cylinder. They are pushed to the lowerperipheral speed driving roll 28 and the higher peripheral speed drivingroll 32, respectively, with adequate pressure. Then, the nip rolls 34,36 rotate at the same peripheral speed with the lower peripheral speeddriving roll 28 and the higher peripheral speed driving roll 32,respectively.

FIG. 3 is a partial enlarged view to illustrate the relationship amongthe lower peripheral speed driving roll 28, the follower roll 30 and thehigher peripheral speed driving roll 32. The first rolling deformationpoint X, which are extending in parallel to the axis of the roll, isformed between the lower peripheral speed driving roll 28 and thefollower roll 30. The second deformation point Y is formed between thehigher peripheral speed driving roll 32 and the follower roll 30.

The lower peripheral speed driving roll 28 is driven in the direction ofan arrow A with at a peripheral speed V₁ and the higher peripheral speeddriving roll 32 is driven in the direction of an arrow C at a peripheralspeed V₃. The follower roll 30 is driven to rotate by the rotation ofdriving rolls 28 and 32 in the direction of an arrow B at a peripheralspeed V₂ with interposing the plastic film 26. The relation among theabove speeds V₁ and V₃ and the speed of follower roll V₂ is expressed byan equation of V₁ <V₂ <V₃.

Comparative rolling tests have been carried out using a rollingapparatus formed with such features in accordance with the presentinvention together with a prior art rolling apparatus and followingresults were obtained. Table 1 shows the results obtained when a highdensity poly-ethylene (HDPE, 60 μm thickness) was used as a filmmaterial and Table 2, polypropylene (PP, 60 μm thickness) and Table 3,polypropylene (PP, 100 μm thickness), respectively.

In these tables, the comparative examples relate to the prior art havingonly one rolling deformation point. Example 1 of the present inventionrelates to a test using a rolling apparatus employing two pairs of rollsas shown in FIG. 7 which will be described later on. Example 2 of thepresent invention relates to a test using a rolling apparatus with threesuccessive rolls as shown in FIG. 3. V₀ is the peripheral speed of thepreheating rolls 21 and 22 as shown in FIG. 1.

The surface property and the reduction of width are evaluated by thefollowing criteria. Surface Properties:

O: The whole is uniformly transparent.

Δ: Striped patterns due to uneven deformation are observed depending onthe angle of reflection

X: Striped patterns are apparently observed or opaque portions are leftReduction of Width:

O: The reduction of width of film material is not more than 10%

Δ: The reduction of width of film material is from 10% to 15%

X: The reduction of width of film material is more than 15%

                  TABLE 1                                                         ______________________________________                                        (HDPE of 60 μm thick)                                                                Comp. Example                                                                             Example 1                                                                              Example 2                                      ______________________________________                                        V.sub.0     2 m/min       2 m/mim    2 m/min                                  V.sub.1     6 m/min       3 m/mim    2 m/min                                  V.sub.2     6 m/min       4 m/mim  2.7 m/min                                  V.sub.3                   6 m/mim    6 m/min                                  V.sub.4                   5 m/mim                                             Evaluation                                                                    Surface Property                                                                          0             0        0                                          Width Reduction                                                                           X             Δ  0                                          ______________________________________                                    

According to the results shown in Table 1, in Example 1 of the presentinvention, two stage rolling was carried out under the conditions thatthe ratios of the peripheral speed were 3/4 at the first rollingdeformation point X and 5/6 at the second rolling deformation point Y.In Example 2, two stage rolling was carried out under the conditionsthat the ratios of the peripheral speed were 2/2.7 at the first rollingdeformation point X and 2.7/6 at the second rolling deformation point Y.

                  TABLE 2                                                         ______________________________________                                        (PP of 60 μm thick)                                                                  Comp. Example                                                                             Example 1                                                                              Example 2                                      ______________________________________                                        V.sub.0     2 m/min       2 m/mim    2 m/min                                  V.sub.1     6 m/min       3 m/mim    2 m/min                                  V.sub.2     6 m/min       4 m/mim  3.7 m/min                                  V.sub.3                   6 m/mim    6 m/min                                  V.sub.4                   5 m/mim                                             Evaluation                                                                    Surface Property                                                                          Δ       0        0                                          Width Reduction                                                                           X             Δ  0                                          ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        (PP of 100 μm thick)                                                               Comp. Example                                                                             Example 1 Example 2                                       ______________________________________                                        V.sub.0    2 m/min        2 m/mim   2 m/min                                   V.sub.1   10 m/min        2 m/mim   2 m/min                                   V.sub.2   10 m/min      3.8 m/mim 5.4 m/min                                   V.sub.3                 6.4 m/mim  10 m/min                                   V.sub.4                  10 m/mim                                             Evaluation                                                                    Surface Property                                                                        Forming was   Δ   X                                                     impossible                                                          Width Reduction                                                                         Tearing occurred                                                                            0         0                                           ______________________________________                                    

In Table 2, the test results obtained using the rolls driven at the sameperipheral speeds as those in Table 1 are shown. However, in Example 2of the present invention, the peripheral speed V₂ of the follower middleroll 30 was 3.7 m/min.

In Example 1 of the present invention shown in Table 3, two stagerolling was carried out under the conditions that the ratios of theperipheral speeds were 2/3.8 at the first rolling deformation point Xand 6.4/10 at the second rolling deformation point Y. In Example 2 ofthe present invention, the peripheral speeds of the driving rolls were 2m/min and 10 m/min, respectively, while the peripheral speed V₂ of thefollower middle roll 30 was 5.4 m/min. Accordingly, the two stagerolling was carried out under the conditions that the ratios of theperipheral speeds were 2/5.4 at the first rolling deformation point Xand 5.4/10 at the second rolling deformation point Y.

Even though it may be considered that the follower roll 30 is notrotated because it is sandwiched between the high speed roll 28 and lowspeed roll 32 which are driven at different peripheral speeds, thefollower roll 30 can be rotated in a stable condition at the peripheralspeed V₂ with a relationship of V₁ <V₂ <V₃, during the practical rollingoperation of a plastic film. The peripheral speed V₂ varies with thetypes of the plastic film to be rolled. But it was unexpectedly foundout that the follower roll 30 is able to rotate in a stable condition ata certain peripheral speed provided that constant processing conditionsare determined.

From the forgoing results, according to the present invention, it ispossible to improve the surface properties by preventing the occurrenceof wrinkles, the change of transparency and the reduction of width ofplastic film 26 after the rolling even in a operation with increasedrolling ratio. In addition, it is possible to apply smaller rollingpressure in each rolling step as compared with the conventional singlestage rolling. As a result, the load imposed on each roll is lowered andthe deflection of the roll is reduced.

It is also possible to make the diameter of roll smaller and the length,longer, so that the material having lower hardness can be used formaking rolls. Therefore, it becomes possible to carry out the rolling ofa plastic film having broader width. This contributes to expand thepossibility in the selection of raw materials to be rolled and toimprove the productivity. In addition, the smaller roll deflectionserves to improve the quality of rolling caused by the deformation ofrolls. Small diameter rolls enable to make the size and, particularly,the weight of rolling apparatus small and, as a result, the effect ofrolling deformation can be improved because of the large curvature ofrolls. In other words, even in the rolling formation of continuousfilms, not only the deformation at a deformation point in rolling butalso the partial deformation by stretching due to the tension caused bythe speed difference between rolls take place and the ratio of thedeformation by rolling can be made larger as the curvature becomeslarger. Particularly with the construction shown in FIG. 1, because themultistage rolling operation is possible with one set of pressingmechanism, such a multistage rolling operation does not lead to raise inthe equipment cost.

The materials used for making rolls are required to be strong enough towithstand the stress of rolled materials in the rolling deformation andgenerally are selected from hard materials. Meanwhile, in the rolling ofa plastic film, the interaction between the surfaces of roll and film,friction coefficient, adhesion property, slipperiness, and the likeproperties greatly affect on the stability in the rolling operation. Itis required to select a suitable material in view of these properties.However, it has often been difficult in the prior art to select adesired material because of the presence of the excessive limitation inthe hardness.

It is important that the follower middle roll 30 can be rotated freelyin view of the stability of rolling operation. When two stage rolling iscarried out under the condition that the same pressing forces areapplied, the rolling ratio at the first rolling deformation point X isdifferent from the rolling ratio at the second rolling deformation pointY and the ratio of them can not be constant but it is varied with thetypes of the plastic films and rolling conditions.

The plastic film entering the second deformation point Y shows theresistance against the rolling deformation which is different from thatof the plastic film entering the first rolling deformation point X. Asone of the major changes, it resists against the additional longitudinaldeformation because the tying molecules connecting crystals arestretched by tension in the longitudinal direction due to thedeformation received at the first rolling deformation point X. Inaddition, the changes in the degree of crystallinity through collapsingand rearrangement of crystals, and transition of the high-orderstructure to another structure may occur by the deformation at the firstdeformation point X, which also affect the resistance against therolling deformation. When the size of crystals or the high-orderstructure are relatively large, the resistance against such deformationas to reduce the film thickness below a certain level may be increasedbecause the deformation of the these high-order structure is limited bythe thickness.

Accordingly, when the same pressing force is applied, depending on thebalance of the rolling at the two rolling deformation points, the ratioof the rolling ratio at the first rolling deformation point to therolling ratio at the second rolling deformation point may vary. If themiddle roll 30 is a driving roll rotating at certain peripheral speed,it is not possible to obtain stably a good product unless the roll iscontrolled by calculating the roll speed. This procedure is quitetroublesome and if the roll speed is not proper, the film may be tornoff or loosened on the middle roll and it will be dragged into therolling deformation point.

In the embodiment as shown in FIG. 3, the peripheral speed V₂ of thefollower middle roll 30 is varied according to the types of plasticfilms 26 to be rolled or the rolling conditions and it will rotate at aconstant and stable speed for a specific plastic film 26 and specificrolling conditions. That is, the ratio of the rolling ratio at the firstrolling deformation point to the rolling ratio at the second rollingdeformation point is automatically controlled so as to be adapted to thetypes of plastic film 26 to be rolled and rolling conditions. Therefore,it is not necessary to carry out troublesome calculation in order todetermine the optimum peripheral speeds to drive the follower middleroll 30, but it is rather desirable to allow roller to be non-poweredand to rotate freely.

Moreover, in FIG. 3, one side surface of the plastic film 26 is denotedas P and the other side surface, as Q. The follower middle roll 30having higher peripheral speed than the lower peripheral speed drivingroll 28 act on the one side surface P of the plastic film 26 at thefirst rolling deformation point X. The higher peripheral speed drivingroll 32 which has higher peripheral speed than the follower roll 30 acton the other side surface Q of the plastic film 26 at the second rollingdeformation point Y. Thus, the one side surface P and the other sidesurface Q of the plastic film 26 alternately receive tensile stresses,thereby preventing the formation of curls in the plastic film, whichcurls were caused to occur in the conventional rolling employing asingle rolling deformation point.

FIG. 4 illustrates a front view of a first modification of the rollingdevice as shown in FIG. 3. Likewise the rolling apparatus shown in FIG.3, this rolling device includes a lower speed driving roll 28 which isrotated at a peripheral speed V₁, a higher speed driving roll 32 whichis rotated at a peripheral speed V₃, and a follower roll 30 which isdriven at a peripheral speed V₂ by means of the contact with thesedriving rolls 28 and 32. The lower speed driving roll 28 and the higherspeed driving roll 32 are rotatably supported to fixed positions,respectively, while the follower roll 30 is rotatably supported by asupporting means 60 which is movable, for example, in the directionshown by an arrow D so as to approach to or get apart from these drivingrolls 28 and 32. Thus, this supporting means 60 provides the pressingforce. The follower roll 30 may be made smaller in size than the drivingrolls 28 and 32, so that the structure of the rolling apparatus as awhole can be made simple as compared with the structure of the rollingapparatus employing the mechanism in which the driving rolls 28 and 32are movably supported.

FIG. 5 illustrates a front view of a second modification of the rollshown in FIG. 3. This squeezing roll like the rolling apparatus shown inFIG. 3 includes the lower speed driving roll 28 which is driven at theperipheral speed V₁, the higher speed driving roll 32 which is driven atthe peripheral speed V₃. Two follower rolls 30b, 30c are disposedbetween these driving rolls 28, 32. The two follower rolls 30b, 30c aredriven by the driving rolls 28, 32, respectively and also driven by thecounterpart follower rolls 30c, 30b, respectively. Thus, the respectiveperipheral speeds V21, V22 of the follower rolls 30b, 30c are differenteach other. Therefore, three rolling deformation points X, Y, Z areformed in this rolling apparatus, which enable rolling operation withreduced rolling ratio and rolling pressure at each stage.

FIG. 6 is a front view of a third modification of the pressing roll asshown in FIG. 3. This roll includes a lower peripheral speed drivingroll 28, a follower roll 30 and a higher peripheral speed driving roll32 as well as a lower peripheral speed driving roll 28h, a follower roll30h and a higher peripheral speed driving roll 32h, each of which arearranged in series. In this rolling apparatus, four rolling deformationpoints are formed, so that the rolling operation can be done with lowerrolling ratios and rolling pressures at the respective stages.

FIG. 7 and FIG. 8 illustrate front views of roll arrangements, each ofwhich consists of paired even number of rolls. In these rolls, all therolls are driving rolls.

In FIG. 7, two pairs of rolls 70 and 72, and 74 and 76 are disposedalong the passage of the plastic film 26. The first pair of the rolls 70and 72 form a first rolling deformation point X and a press-down means(not shown) pushes down one roll 70 toward the other side roll 72 asindicated by an arrow G. The peripheral speed V₁ of the roll 70 on oneside (upside) is small than the peripheral speed V₂ of the roll 72 onthe other side (downside). Likewise, the second pair of the rolls 74 and76 form the second rolling deformation point and a press-down means (notshown) pushes one roll 74 toward the other side roll 76 as shown by anarrow H. The peripheral speed V₃ of the roll 74 on one side (upside) islarger than the peripheral speed V₄ of the other side (downside) roll76.

The plastic film 26 has a one side surface P and the other side surfaceQ. Also in this case, the downside roll 72 having a higher peripheralspeed acts on the other side surface Q of the plastic film 26 at thefirst rolling deformation point X. The upside roll 74 having higherperipheral speed acts on the one side surface P of the plastic film 26at the second rolling deformation point Y. Thus, the one side surface Pand the other side surface Q of the plastic film 26 alternately receivetensile stresses, thereby enabling to prevent the curling of the plasticfilm which was caused to occur in the prior art rolling operationadopting a single rolling deformation point.

In FIG. 8, three pairs of rolls 70 and 72; 74 and 76; and 78 and 80 aredisposed along the passage of the plastic film 26. The press-down means(not shown) provides pressing down force to the respective pairs of therolls 70 and 72; 74 and 76; and 78 and 80 as shown by arrows G, H and I.Other features in this example are the same as those described in theexample as shown in FIG. 7. That is, in the rolls 70, 72, 74 and 76, theperipheral speed V₁ is smaller than V₂ at the rolling deformation pointX and the peripheral speed V₃ is larger than V₄ at the rollingdeformation point Y. In the rolls 78 and 80, the peripheral speed V₅ issmaller than V₆ at the rolling deformation point Z.

Industrial Applicability

As described above, according to the present invention, it is possibleto manufacture a quality wrinkleless plastic film without the reductionof width with high productivity.

We claim:
 1. A rolling apparatus for a plastic film which if providedwith at least three rolls disposed along the passage of said plasticfilm, wherein a plurality of rolling deformation points are formedbetween adjacent rolls so as to subject said plastic film to stepwiserolling with said rolls, an upstream roll and a downstream roll of saidat least three rolls are driving rolls, at least one intermediate rollbetween said upstream roll and said downstream roll of said at leastthree rolls comprising at least one follower roll; including drivingmeans for driving said driving rolls, wherein adjacent two of said rollsat one deformation point are rotated in such a manner that theperipheral speed of the roll on one side of the film is larger than theperipheral speed of the roll on the other side of the film, and twoother adjacent rolls at the successive deformation point are rotatedsuch that the peripheral speed of the roll on said one side of the filmis smaller than the speed of the roll on the other side of the film. 2.A rolling apparatus for a plastic film as claimed in claim 1, whereinsaid apparatus is equipped with press-down means in order to impart adownward pressing force to push one of said two driving rolls towardanother roll.
 3. A rolling apparatus for a plastic film as claimed inclaim 1, wherein said apparatus is equipped with a pressing means inorder to impart a pressing force for rolling by pushing said followerroll or rolls toward said two driving rolls.
 4. A rolling apparatus forplastic film which comprises:an upstream side driving roll, a downstreamside driving roll which is rotated at a peripheral speed higher thanthat of said upstream side driving roll, a follower roll which forms anupstream side rolling deformation point with said upstream side drivingroll to effect rolling of a plastic film while forming a downstream siderolling deformation point with said downstream side driving roll toeffect further rolling of the plastic film once rolled at said upstreamside rolling deformation point; including driving means for driving saiddriving rolls, wherein adjacent two of said rolls at one deformationpoint are rotated in such a manner that the peripheral speed of the rollon one side of the film is larger than the peripheral speed of the rollon the other side of the film, and two other adjacent rolls at thesuccessive deformation point are rotated such that the peripheral speedof the roll on said one side of the film is smaller than the speed ofthe roll on the other side of the film.
 5. A rolling apparatus for aplastic film which comprises:an upstream side driving roll, a downstreamside driving roll which is rotated at a peripheral speed higher thanthat of the upstream side driving roll, an upstream side follower rollwhich forms an upstream side rolling deformation point with saidupstream side driving roll to effect rolling of a plastic film, adownstream side follower roll which forms a middle rolling deformationpoint with said upstream side follower roll further effect rolling ofthe plastic film once rolled at said upstream side rolling deformationpoint while forming a downstream side rolling deformation point withsaid downstream side driving roll still further to effect rolling of theplastic film rolled at said middle rolling deformation point; includingdriving means for driving said driving rolls, wherein adjacent two ofsaid rolls at one deformation point are rotated in such a manner thatthe peripheral speed of the roll on one side of the film is larger thanthe peripheral speed of the roll on the other side of the film, and twoother adjacent rolls at the successive deformation point are rotatedsuch that the peripheral speed of the roll on said one side of the filmis smaller than the speed of the roll on the other side of the film.